In living hepatic parenchymal cells are enzyme systems responsible for the metabolism of compounds foreign to the organism. Oxidation of a variety of xenobiotics results in the formation of products which in themselves can be toxic to the organisms. One class of products are the aldehydes, for example, acetaldehyde arising from ethanol metabolism, SKF 525-A metabolism and other de-ethylation reactions; formaldehyde arises from N-demethylation of a number of drugs like aminopyrine, codeine, ethylmorphine, etc. These aldehydes are apparently channeled from the endoplasmic reticulum into the mitochondria for further degradation. Krebs cycle substrates, like succinate, apparently stimulate N-demethylation in the presence of mitochondria and microsomes by lowering the level of intramitochondrial of NAD plus, resulting in the inhibition of aldehyde (HCHO) dehydrogenase activity. Hence the mitochrondrial/microsomal organelle interaction involves 2 separate enzyme systems operating in synchrony. The proposed research will involve characterization of the aldehyde dehydrogenase system with respect to localization, biochemical properties such as pH optimum, Km and Vmax for substrates and cofactor, substrate specificity, etc. Attempts to isolate the enzyme and purification of the latter will be pursued.